Six degree of freedom alignment display for medical procedures

ABSTRACT

A display and navigation system for use in guiding a medical device to a target in a patient includes a tracking sensor, a tracking device and display. The tracking sensor is associated with the medical device and is used to track the medical device. The tracking device tracks the medical device with the tracking sensor. The display includes indicia illustrating at least five degree of freedom information and indicia of the medical device in relation to the five degree of freedom information.

FIELD OF THE INVENTION

The present invention generally relates to displays for use in medicalprocedures, and more specifically, to a six degree of freedom alignmentdisplay that includes indicia of the six degrees of freedom to assist inperforming medical procedures.

BACKGROUND OF THE INVENTION

Image guided medical and surgical procedures utilize patient imagesobtained prior to or during a medical procedure to guide a physicianperforming the procedure. Recent advances in imaging technology,especially in imaging technologies that produce highly-detailed,computer-generated two-dimensional and three-dimensional images, such ascomputed tomography (CT), magnetic resonance imaging (MRI), isocentricC-arm fluoroscopic imaging or two and three-dimensional fluoroscopes orultrasounds have increased the interest in image guided medicalprocedures.

During these image guided medical procedures, the area of interest ofthe patient that has been imaged is displayed on a two-dimensionaldisplay. Surgical instruments that are used during this medicalprocedure are tracked and superimposed onto this two-dimensional displayto show the location of the surgical instrument relative to the area ofinterest in the body. However, these two-dimensional displays are notcapable of providing either five or six degrees of freedom informationof the instrument or other devices navigated in the body, which may beinformation in certain medical procedures.

Other types of navigation systems operate as an image-less system, wherean image of the body is not captured by an imaging device prior to themedical procedure. With this type of procedure, the system may use aprobe to contact certain landmarks in the body, such as landmarks onbone, where the system generates either a two-dimensional orthree-dimensional model of the area of interest based upon thesecontacts. This way, when the surgical instrument or other object istracked relative to this area, they can be superimposed on this model.Here again, however, the display that illustrates the tracked medicalinstrument in relation to this model is not capable of providing five orsix degree of freedom information.

Moreover, in certain medical procedures providing either a five or sixdegree of freedom display, will greatly assist the surgeon in themedical procedure. For example, this type of information may be helpfulwith minimally invasive procedures where clearance and viewing of thearea of interest may not be relatively available. Therefore, duringthese types of procedures, the surgeon may not clearly know where thetip or orientation of the instrument may be relative to the patient.With flexible instruments, such as catheters, it makes it even moredifficult to estimate where the tip or orientation of the catheter maybe during these types of procedures.

Still other procedures, such as orthopedic procedures, employ implantsthat include multiple components that articulate with one another.Placement of one component of the implant relative to another componentof the implant is critical. If a display can provide both targeting andsix degree of freedom information in relation to these mutuallydependent components, these procedures may be improved. For example,each implant component may require a specific orientation relative toits corresponding implant component to provide for the proper placementand proper range of motion. With these types of procedures and implants,it is generally difficult to accurately locate the components in thefive or six degrees of freedom position. Since the orientation andlocation of these individual components is dependent upon one another tobe effective, these components must be properly positioned and alignedin order to improve the life of the implant, increase the range ofmotion and provide superior patient outcomes.

It is, therefore, desirable to provide a display, which can provide fiveor six degrees of freedom alignment information regarding trackedsurgical instruments and implants, particularly implants or devices thathave several components each having a specific orientation dependentupon one another. It is, therefore, an object of the present inventionto provide such a display to assist in medical procedures.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a six degreeof freedom alignment display that includes indicia of at least fivedegree of freedom information to assist in performing a medicalprocedure is disclosed. The six degree of freedom display assists invarious types of medical procedures, including orthopedic procedures,neurovascular, intravascular, spinal, cardiovascular procedures, softtissue procedures, etc.

In an embodiment, a display for use in guiding a medical device to atarget in a patient during a medical procedure includes indicia. Thisindicia includes first, second, third, fourth, and fifth indiciaillustrated on the display that identifies first, second, third, fourth,and fifth degree of freedom information. These indicias are illustratedon the display to assist in guiding the medical device to the target.

In another embodiment, a navigation system for use in guiding a medicaldevice to a target in a patient during a medical procedure includes atracking sensor, a tracking device and a display. The tracking sensor isassociated with the medical device and is operable to be used to trackthe medical device. The tracking device is operable to track the medicaldevice with the tracking sensor. The display includes indiciaillustrating at least five degree of freedom information and indicia ofthe medical device in relation to the at least five degree of freedominformation.

In yet another embodiment, a method for navigation and displaying amedical device during a medical procedure is provided. This methodincludes selecting a target for navigating the medical device to,displaying the target in a coordinate system, tracking the medicaldevice, and displaying the medical device in relation to the target withat least five degree of freedom information.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a diagram of a navigation system employing the displayaccording to the teachings of the present invention;

FIGS. 2 a and 2 b are diagrams representing undistorted and distortedviews of a fluoroscopic C-arm imaging device;

FIGS. 3 a and 3 b is a logic block diagram illustrating a method foremploying the display according to the teachings of the presentinvention;

FIGS. 4 a-4 e illustrate a medical procedure employing the displayaccording to the teachings of the present invention;

FIG. 5 is a figure of the display according to the teachings of thepresent invention;

FIG. 6 is a split screen view of the display according to the teachingsof the present invention;

FIG. 7 is an additional split screen view of the display according tothe teachings of the present invention;

FIGS. 8 a-8 g illustrate another medical procedure employing the displayaccording to the teachings of the present invention; and

FIG. 9 is an illustration of a dual display according to the teachingsof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. Moreover, while the invention is discussed indetail below in regard to an orthopedic surgical procedure, the displayof the present invention may be used with any type of medical procedure,including orthopedic, cardiovascular, neurovascular, soft tissueprocedures, or any other medical procedures.

FIG. 1 is a diagram illustrating the five or six degree of freedom (5 or6 DOF) alignment display 10 employed with an image guided navigationsystem 12 for use in navigating a surgical instrument or implant duringa medical procedure. It should also be noted that the display 10 of thepresent invention may be used or employed in an image-less basednavigation system, further discussed herein. The navigation system 12may be used to navigate any type of instrument or delivery system, suchas a reamer, impactor, cutting block, saw blade, catheter, guide wires,needles, drug delivery systems, and cell delivery systems. Thenavigation system 12 may also be used to navigate any type of implantincluding orthopedic implants, spinal implants, cardiovascular implants,neurovascular implants, soft tissue implants, or any other devicesimplanted in a patient 14. The navigation system 12 may also be used tonavigate implants or devices that are formed as an assembly or frommultiple components where the location and orientation of each componentis dependent upon one another to be effective in its use. For example,during a spinal procedure, the display may be used to track and align aspinal screw with a spinal rod to insure attachment of each device.

The navigation system 12 includes an imaging device 16 that is used toacquire pre-operative or real-time images of the patient 14. The imagingdevice 16 is a fluoroscopic C-arm x-ray imaging device that includes aC-arm 18, an x-ray source 20, an x-ray receiving section 22, an optionalcalibration and tracking target 24 and optional radiation sensors 26.The optional calibration and tracking target 24 includes calibrationmarkers 28 (see FIGS. 2 a-2 b), further discussed herein. A C-armcontroller 30 captures the x-ray images received at the receivingsection 22 and stores the images for later use. The C-arm controller 30may also control the rotation of the C-arm 18. For example, the C-arm 18may move in the direction of arrow 32 or rotate about the long axis ofthe patient 14, allowing anterior or lateral views of the patient 14 tobe imaged. Each of these movements involve rotation about a mechanicalaxis 34 of the C-arm 18. In this example, the long axis of the patient14 is substantially in line with the mechanical axis 34 of the C-arm 18.This enables the C-arm 18 to be rotated relative to the patient 14,allowing images of the patient 14 to be taken from multiple directionsor about multiple planes. An example of a fluoroscopic C-arm x-rayimaging device 16 is the “Series 9600 Mobile Digital Imaging System,”from OEC Medical Systems, Inc., of Salt Lake City, Utah. Other exemplaryfluoroscopes include bi-plane fluoroscopic systems, ceiling fluoroscopicsystems, cath-lab fluoroscopic systems, fixed C-arm fluoroscopicsystems, etc.

In operation, the imaging device 16 generates x-rays from the x-raysource 20 that propagate through the patient 14 and calibration and/ortracking target 24, into the x-ray receiving section 22. The receivingsection 22 generates an image representing the intensities of thereceived x-rays. Typically, the receiving section 22 includes an imageintensifier that first converts the x-rays to visible light and a chargecoupled device (CCD) video camera that converts the visible light intodigital images. Receiving section 22 may also be a digital device thatconverts x-rays directly to digital images, thus potentially avoidingdistortion introduced by first converting to visible light. With thistype of digital C-arm, which is generally a flat panel device, thecalibration and/or tracking target 24 and the calibration processdiscussed below may be eliminated. Also, the calibration process may beeliminated for different types of medical procedures. Alternatively, theimaging device 16 may only take a single image with the calibration andtracking target 24 in place. Thereafter, the calibration and trackingtarget 24 may be removed from the line-of-sight of the imaging device16.

Two dimensional fluoroscopic images taken by the imaging device 16 arecaptured and stored in the C-arm controller 30. These images areforwarded from the C-arm controller 30 to a controller or work station36 having the display 10 that may either include a single display 10 ora dual display 10 and a user interface 38. The work station 36 providesfacilities for displaying on the display 10, saving, digitallymanipulating, or printing a hard copy of the received images, as well asthe five or six degree of freedom display. The user interface 38, whichmay be a keyboard, joy stick, mouse, touch pen, touch screen or othersuitable device allows a physician or user to provide inputs to controlthe imaging device 16, via the C-arm controller 30, or adjust thedisplay settings, such as safe zones of the display 10, furtherdiscussed herein. The work station 36 may also direct the C-armcontroller 30 to adjust the rotational axis 34 of the C-arm 18 to obtainvarious two-dimensional images along different planes in order togenerate representative two-dimensional and three-dimensional images.When the x-ray source 20 generates the x-rays that propagate to thex-ray receiving section 22, the radiation sensors 26 sense the presenceof radiation, which is forwarded to the C-arm controller 30, to identifywhether or not the imaging device 16 is actively imaging. Thisinformation is also transmitted to a coil array controller 48, furtherdiscussed herein. Alternatively, a person or physician may manuallyindicate when the imaging device 16 is actively imaging or this functioncan be built into the x-ray source 20, x-ray receiving section 22, orthe control computer 30.

Fluoroscopic C-arm imaging devices 16 that do not include a digitalreceiving section 22 generally require the calibration and/or trackingtarget 24. This is because the raw images generated by the receivingsection 22 tend to suffer from undesirable distortion caused by a numberof factors, including inherent image distortion in the image intensifierand external electromagnetic fields. An empty undistorted or ideal imageand an empty distorted image are shown in FIGS. 2 a and 2 b,respectively. The checkerboard shape, shown in FIG. 2 a, represents theideal image 40 of the checkerboard arranged calibration markers 28. Theimage taken by the receiving section 22, however, can suffer fromdistortion, as illustrated by the distorted calibration marker image 42,shown in FIG. 2 b.

Intrinsic calibration, which is the process of correcting imagedistortion in a received image and establishing the projectivetransformation for that image, involves placing the calibration markers28 in the path of the x-ray, where the calibration markers 28 are opaqueor semi-opaque to the x-rays. The calibration markers 28 are rigidlyarranged in pre-determined patterns in one or more planes in the path ofthe x-rays and are visible in the recorded images. Because the truerelative position of the calibration markers 28 in the recorded imagesare known, the C-arm controller 30 or the work station or computer 36 isable to calculate an amount of distortion at each pixel in the image(where a pixel is a single point in the image). Accordingly, thecomputer or work station 36 can digitally compensate for the distortionin the image and generate a distortion-free or at least a distortionimproved image 40 (see FIG. 2 a). A more detailed explanation ofexemplary methods for performing intrinsic calibration are described inthe references: B. Schuele, et al., “Correction of Image IntensifierDistortion for Three-Dimensional Reconstruction,” presented at SPIEMedical Imaging, San Diego, Calif. 1995; G. Champleboux, et al.,“Accurate Calibration of Cameras and Range Imaging Sensors: the NPBSMethod,” Proceedings of the IEEE International Conference on Roboticsand Automation, Nice, France, May, 1992; and U.S. Pat. No. 6,118,845,entitled “System And Methods For The Reduction And Elimination Of ImageArtifacts In The Calibration Of X-Ray Imagers,” issued Sep. 12, 2000,the contents of which are each hereby incorporated by reference.

While the fluoroscopic C-arm imaging device 16 is shown in FIG. 1, anyother alternative imaging modality may also be used or an image-lessbased application may also be employed, as further discussed herein. Forexample, isocentric fluoroscopy, bi-plane fluoroscopy, ultrasound,computed tomography (CT), multi-slice computed tomography (MSCT),magnetic resonance imaging (MRI), high frequency ultrasound (HIFU),optical coherence tomography (OCT), intra-vascular ultrasound (IVUS),2D, 3D or 4D ultrasound, or intraoperative CT or MRI may also be used toacquire pre-operative or real-time images or image data of the patient14. Image datasets from hybrid modalities, such as positron emissiontomography (PET) combined with CT, or single photon emission computertomography (SPECT) combined with CT, could also provide functional imagedata superimposed onto anatomical data to be used to confidently reachtarget sights within the areas of interest. It should further be notedthat the fluoroscopic C-arm imaging device 16, as shown in FIG. 1,provides a virtual bi-plane image using a single-head C-arm fluoroscope16 by simply rotating the C-arm 18 about at least two planes, whichcould be orthogonal planes to generate two-dimensional images that canbe converted to three-dimensional volumetric images that can bedisplayed on the six degree of freedom display 10.

The navigation system 12 further includes an electromagnetic navigationor tracking system 44 that includes a transmitter coil array 46, thecoil array controller 48, a navigation probe interface 50, an instrument52 having an electromagnetic tracker and a dynamic reference frame 54.It should further be noted that the entire tracking system 44 or partsof the tracking system 44 may be incorporated into the imaging device16, including the work station 36 and radiation sensors 26.Incorporating the tracking system 44 will provide an integrated imagingand tracking system. Any combination of these components may also beincorporated into the imaging system 16, which again can include afluoroscopic C-arm imaging device or any other appropriate imagingdevice. Obviously, if an image-less procedure is performed, thenavigation and tracking system 44 will be a stand alone unit.

The transmitter coil array 46 is shown attached to the receiving section22 of the C-arm 18. However, it should be noted that the transmittercoil array 46 may also be positioned at any other location as well,particularly if the imaging device 16 is not employed. For example, thetransmitter coil array 46 may be positioned at the x-ray source 20,within the OR table 56 positioned below the patient 14, on siderailsassociated with the OR table 56, or positioned on the patient 14 inproximity to the region being navigated, such as by the patient's pelvicarea. The transmitter coil array 46 includes a plurality of coils thatare each operable to generate distinct electromagnetic fields into thenavigation region of the patient 14, which is sometimes referred to aspatient space. Representative electromagnetic systems are set forth inU.S. Pat. No. 5,913,820, entitled “Position Location System,” issuedJun. 22, 1999 and U.S. Pat. No. 5,592,939, entitled “Method and Systemfor Navigating a Catheter Probe,” issued Jan. 14, 1997, each of whichare hereby incorporated by reference.

The transmitter coil array 46 is controlled or driven by the coil arraycontroller 48. The coil array controller 48 drives each coil in thetransmitter coil array 46 in a time division multiplex or a frequencydivision multiplex manner. In this regard, each coil may be drivenseparately at a distinct time or all of the coils may be drivensimultaneously with each being driven by a different frequency. Upondriving the coils in the transmitter coil array 46 with the coil arraycontroller 48, electromagnetic fields are generated within the patient14 in the area where the medical procedure is being performed, which isagain sometimes referred to as patient space. The electromagnetic fieldsgenerated in the patient space induces currents in sensors 58 positionedin the instrument 52, further discussed herein. These induced signalsfrom the instrument 52 are delivered to the navigation probe interface50 and subsequently forwarded to the coil array controller 48. Thenavigation probe interface 50 provides all the necessary electricalisolation for the navigation system 12. The navigation probe interface50 also includes amplifiers, filters and buffers required to directlyinterface with the sensors 58 in instrument 52. Alternatively, theinstrument 52 may employ a wireless communications channel as opposed tobeing coupled directly to the navigation probe interface 50.

The instrument 52 is equipped with at least one, and may includemultiple localization sensors 58. In this regard, the instrument 52 mayinclude an orthogonal pair coil sensor 58 or a tri-axial coil sensor 58or multiple single coil sensors 58 positioned about the instrument 52.Here again, the instrument 52 may be any type of medical instrument orimplant. For example, the instrument may be a catheter that can be usedto deploy a medical lead, be used for tissue ablation, or be used todeliver a pharmaceutical agent. The instrument 52 may also be anorthopedic instrument, used for an orthopedic procedure, such asreamers, impactors, cutting blocks, saw blades, drills, etc. Theinstrument 52 may also be any type of neurovascular instrument,cardiovascular instrument, soft tissue instrument, etc. Finally, theinstrument 52 may be an implant that is tracked, as well as any othertype of device positioned and located within the patient 14. Theseimplants can include orthopedic implants, neurovascular implants,cardiovascular implants, soft tissue implants, or any other devices thatare implanted into the patient 14. Particularly, implants that areformed from multiple components where the location and orientation ofeach component is dependent upon the location and orientation of theother component, such that each of these components can be tracked ornavigated by the navigation and tracking system 44 to be displayed onthe six degree of freedom display 10.

In an alternate embodiment, the electromagnetic sources or generatorsmay be located within the instrument 52 and one or more receiver coilsmay be provided externally to the patient 14 forming a receiver coilarray similar to the transmitter coil array 46. In this regard, thesensor coils 58 would generate electromagnetic fields, which would bereceived by the receiving coils in the receiving coil array similar tothe transmitter coil array 46. Other types of localization or trackingmay also be used with other types of navigation systems, which mayinclude an emitter, which emits energy, such as light, sound, orelectromagnetic radiation, and a receiver that detects the energy at aposition away from the emitter. This change in energy, from the emitterto the receiver, is used to determine the location of the receiverrelative to the emitter. These types of localization systems includeconductive, active optical, passive optical, ultrasound, sonic,electromagnetic, etc. An additional representative alternativelocalization and tracking system is set forth in U.S. Pat. No.5,983,126, entitled “Catheter Location System and Method,” issued Nov.9, 1999, which is hereby incorporated by reference. Alternatively, thelocalization system may be a hybrid system that includes components fromvarious systems.

The dynamic reference frame 54 of the electromagnetic tracking system 44is also coupled to the navigation probe interface 50 to forward theinformation to the coil array controller 48. The dynamic reference frame54 is a small magnetic field detector or any other type ofdetector/transmitter that is designed to be fixed to the patient 14adjacent to the region being navigated so that any movement of thepatient 14 is detected as relative motion between the transmitter coilarray 46 and the dynamic reference frame 54. This relative motion isforwarded to the coil array controller 48, which updates registrationcorrelation and maintains accurate navigation, further discussed herein.The dynamic reference frame 54 can be configured as a pair oforthogonally oriented coils, each having the same center or may beconfigured in any other non-coaxial coil configuration. The dynamicreference frame 54 may be affixed externally to the patient 14, adjacentto the region of navigation, such as the patient's pelvic region, asshown in FIG. 1 or on any other region of the patient. The dynamicreference frame 54 can be affixed to the patient's skin, by way of astick-on adhesive patch. The dynamic reference frame 54 may also beremovably attachable to fiducial markers 60 also positioned on thepatient's body and further discussed herein.

Alternatively, the dynamic reference frame 54 may be internallyattached, for example, to the pelvis or femur of the patient using bonescrews that are attached directly to the bone. This provides increasedaccuracy since this will track any motion of the bone. Moreover,multiple dynamic reference frames 54 may also be employed to track theposition of two bones relative to a joint. For example, one dynamicreference frame 54 may be attached to the pelvis, while a second dynamicreference frame 54 may be attached to the femur during hip arthroplasty.In this way, motion of the femur relative to the pelvis may be detectedby the dual dynamic reference frames 54. An exemplary dynamic referenceframe 54 and fiducial marker 60, is set forth in U.S. Pat. No.6,381,485, entitled “Registration of Human Anatomy Integrated forElectromagnetic Localization,” issued Apr. 30, 2002, which is herebyincorporated by reference.

Briefly, the navigation system 12 operates as follows. The navigationsystem 12 creates a translation map between all points in theradiological image generated from the imaging device 16 and thecorresponding points in the patient's anatomy in patient space. Afterthis map is established, whenever a tracked instrument 52 is used, thework station 36 in combination with the coil array controller 48 and theC-arm controller 30 uses the translation map to identify thecorresponding point on the pre-acquired image, which is displayed ondisplay 10. This identification is known as navigation or localization.An icon representing the localized point or instrument is shown on thedisplay 10, along with five or six degrees of freedom indicia.

To enable navigation, the navigation system 12 must be able to detectboth the position of the patient's anatomy 14 and the position of thesurgical instrument 52. Knowing the location of these two items allowsthe navigation system 12 to compute and display the position of theinstrument 52 in relation to the patient 14. The tracking system 44 isemployed to track the instrument 52 and the anatomy simultaneously.While the display 10 is configured to show the instrument with sixdegree of freedom accuracy.

The tracking system 44 essentially works by positioning the transmittercoil array 46 adjacent to the patient space to generate a low-energymagnetic field generally referred to as a navigation field. Becauseevery point in the navigation field or patient space is associated witha unique field strength, the electromagnetic tracking system 44 candetermine the position of the instrument 52 by measuring the fieldstrength at the sensor 58 location. The dynamic reference frame 54 isfixed to the patient 14 to identify the location of the patient 14 inthe navigation field. The electromagnetic tracking system 44continuously recomputes the relative position of the dynamic referenceframe 54 and the instrument 52 during localization and relates thisspatial information to patient registration data to enable imageguidance of the instrument 52 within the patient 14.

Patient registration is the process of determining how to correlate theposition of the instrument 52 on the patient 14 to the position on thediagnostic, pre-acquired, or real-time images. To register the patient14, the physician or user will select and store particular points fromthe pre-acquired images and then touch the corresponding points on thepatient's anatomy with a pointer probe 62. The navigation system 12analyzes the relationship between the two sets of points that areselected and computes a match, which correlates every point in the imagedata with its corresponding point on the patient's anatomy or thepatient space. The points that are selected to perform registration arethe fiducial arrays or landmarks 60. Again, the landmarks or fiducialpoints 60 are identifiable on the images and identifiable and accessibleon the patient 14. The landmarks 60 can be artificial landmarks 60 thatare positioned on the patient 14 or anatomical landmarks 60 that can beeasily identified in the image data. The system 12 may also perform 2Dto 3D registration by utilizing the acquired 2D images to register 3Dvolume images by use of contour algorithms, point algorithms or densitycomparison algorithms, as is known in the art.

In order to maintain registration accuracy, the navigation system 12continuously tracks the position of the patient 14 during registrationand navigation. This is necessary because the patient 14, dynamicreference frame 54, and transmitter coil array 46 may all move duringthe procedure, even when this movement is not desired. Therefore, if thenavigation system 12 did not track the position of the patient 14 orarea of the anatomy, any patient movement after image acquisition wouldresult in inaccurate navigation within that image. The dynamic referenceframe 54 allows the electromagnetic tracking device 44 to register andtrack the anatomy. Because the dynamic reference frame 54 is rigidlyfixed to the patient 14, any movement of the anatomy or the transmittercoil array 46 is detected as the relative motion between the transmittercoil array 46 and the dynamic reference frame 54. This relative motionis communicated to the coil array controller 48, via the navigationprobe interface 50, which updates the registration correlation tothereby maintain accurate navigation.

It should also be understood that localization and registration data maybe specific to multiple targets. For example, should a spinal procedurebe conducted, each vertebra may be independently tracked and thecorresponding image registered to each vertebra. In other words, eachvertebra would have its own translation map between all points in theradiological image and the corresponding points in the patient's anatomyin patient space in order to provide a coordinate system for eachvertebra being tracked. The tracking system 44 would track any motion ineach vertebra by use of a tracking sensor 58 associated with eachvertebra. In this way, dual displays 10 may be utilized, furtherdiscussed herein, where each display tracks a corresponding vertebrausing its corresponding translation map and a surgical implant orinstrument 52 may be registered to each vertebra and displayed on thedisplay 10 further assisting an alignment of an implant relative to twoarticulating or movable bones. Moreover, each separate display in thedual display 10 may superimpose the other vertebra so that it ispositioned adjacent to the tracked vertebra thereby adding a furtherlevel of information on the six degree of freedom display 10.

As an alternative to using the imaging system 16, in combination withthe navigation and tracking system 44, the five or six degree of freedomalignment display 10 can be used in an imageless manner without theimaging system 16. In this regard, the navigation and tracking system 44may only be employed and the probe 62 may be used to contact or engagevarious landmarks on the patient. These landmarks can be bony landmarkson the patient, such that upon contacting a number of landmarks for eachbone, the workstation 36 can generate a three-dimensional model of thebones. This model is generated based upon the contacts and/or use ofatlas maps. The workstation 36 may also generate a center axis ofrotation for the joint or planes, based upon the probe contacts.Alternatively, the tracking sensor 58 may be placed on the patient'sanatomy and the anatomy moved and correspondingly tracked by thetracking system 44. For example, placing a tracking sensor 58 on thefemur and fixing the pelvis in place of a patient and rotating the legwhile it is tracked with the tracking system 44 enables the work station36 to generate a center of axis of the hip joint by use of kinematicsand motion analysis algorithms, as is known in the art. If the pelvis isnot fixed, another tracking sensor 58 may be placed on the pelvis toidentify the center of axis of the hip joint. If a tracking sensor 58 isplaced on the femur and a tracking sensor 58 is placed on the tibia,upon moving this portion of the anatomy, a center of axis of the kneejoint may be identified. Likewise, by placing a separate tracking sensor58 on two adjacent vertebra and articulating the spine, the center ofaxis of the spinal region can also be identified. In this way, a targetand/or model based on the center of the particular joint may bedesignated and identified on the six degree of freedom display 10.Movement of the instrument or implant 52 may then be tracked in relationto this target and/or model to properly align the instrument or implant52 relative to the target and/or model.

Turning to FIGS. 3 a and 3 b, the method of employing the six degree offreedom display 10 is described in further detail. The method 64 beginsby determining whether an image based medical procedure will be employedor an image-less medical procedure will be employed. If the image basedprocedure is being employed, the method proceeds along the first branch.In this regard, when an image based procedure will be utilized, themethod begins at block 66 identifying the image tracking procedure. Fromblock 66, the method proceeds to block 68 where images are generated bythe imaging system 16. This imaging is performed at the area of interestof the patient 14 by any type of imaging device as previously discussed.Once images have been generated at block 68, the method proceeds toblock 70 where calibration and registration is performed. In block 70,calibration of the imaging device 16 takes place using the calibrationtargets 28. Additionally, registration of the pre-acquired images fromblock 68 are registered to the patient space of the medical procedureutilizing the fiducial markers 60 and probe 62 as previously discussed.This registration registers the current patient space with thepre-acquired image, so that the instrument 52 or other devices may betracked during the medical procedure and accurately superimposed overthe pre-acquired images generated from the imaging device 16.

If an image-less medical procedure is selected, the method begins atblock 72 identifying that an image-less based medical procedure will beperformed. This method proceeds to either block 74 identifying a firstway to generate image-less models or block 76 identifying a second wayto generate image-less models. At block 74, the probe 62 is used tocontact the body at various anatomical landmarks in the area ofinterest, such as a bone. For example, by touching the probe 62 to thepelvis, knee, and ankle, articulation planes can be defined using knownalgorithms and the center of each joint may also be defined. An exampleof this type of modeling is set forth in U.S. Pat. No. 5,682,886, whichis hereby incorporated by reference. Alternatively, multiple anatomicallandmarks can be contacted with the probe 62 to generate a 3-D modelwith the more points contacted, the more accurate the model depicted.

Secondly, to generate a model at block 76, a tracking device is placedon the body and the body rotated about the joint. When this is done, theplane of rotation and joint center can be identified using knownkinematic and/or motion analysis algorithms or using atlas maps ortables, as is known in the art. Once the area of interest has beenprobed, via block 74 or block 76, a model is generated at block 78. Thismodel can be a 3D surface rendered model, a 2-D model identifyingarticulating planes or a 3D model identifying articulating planes androtation, as well as the center of the joints. This enables the display10 to use the joint centers or articulating planes as the target ortrajectory, further discussed herein.

With each of the procedures 74 or 76, the procedure may be initiallybased on the use of atlas information or a 3-D model that is morphed, tobe a patient specific model. In this regard, should the femur be thearea of interest, an accurate representation of an ordinary femur may beselected from an atlas map, thereby providing an initial 2-D or 3-Dmodel representing a typical anatomical femur. As with block 74, uponcontacting numerous areas on the actual femur with the probe 62, theatlas model may be morphed into a patient specific 3-D model, with themore points contacted, the more accurate the morphed model. Patientspecific information may also be acquired using an ultrasound probe toagain identify the shape of the patient's natural femur in order tomorph the atlas model. A fluoroscopic image of the region may also beused to morph the patient's femur with the atlas model to provide apatient specific morphed model. Proceeding under block 76 and assumingthat the area of interest is the hip joint, an atlas model of the femurand pelvis may be the initial starting point. Upon rotating and movingthe femur relative to the pelvis, a patient specific morphed model maybe created to generate accurate joint centers and axes of motion againusing known kinematics and/or motion analysis algorithms

Once the image data is calibrated and registered at block 70 or themodel is generated at block 78, the method proceeds to block 80. Atblock 80, the specific type of coordinate system is selected, which willbe displayed by indicia on the six degree of freedom display 10. Thecoordinate systems can be a Cartesian coordinate system, a sphericalcoordinate system, or a polar coordinate system. By way of example, theCartesian coordinate system will be selected. The Cartesian coordinatesystem will include the X, Y, and Z axes, and X rotation, Y rotation,and Z rotation about its respective axes.

With reference to FIG. 5, the six degree of freedom display 10 is shownin further detail employing the Cartesian coordinate system. In thisregard, the X axis 82 and the Y axis 84 are shown positioned on thedisplay 10. The Z axis 86 extends out from the display 10 and is shownin the upper left corner. Rotation about the X axis is shown by bargraph 88 to the right of the display 10 and rotation about the Y axis isshown by bar graph 90 positioned at the bottom of the display 10.Rotation about the Z axis is shown with the arcuate bar graph 92oriented about the X and Y axes 82 and 84. Each axis, as well as therotation axes identified by the bar graphs may be color coded toidentify safe zones or regions for the item being tracked or navigated.In this regard, the safe zones can be defined as ranges around theplanned trajectory path or target where the safe zones are determined bymanufactured determined parameters, user determined parameters orpatient specific parameter, further discussed herein.

Arrow indicator 94 identifies the degree of rotation about the X axis82. Arrow indicator 96 shows the amount of rotation about the Y axis 84.Arrow 98 identifies the rotation about the Z axis, while arrow 100identifies the depth being tracked along the Z axis 86. The origin 102may be set to be the desired target position or trajectory path. Thecrosshairs 104 represents the tip of the instrument 52 being tracked,while the circle 106 represents the hind area of the instrument 52 beingtracked. With the understanding that the instrument 52 can be any typeof medical device or implant. Also, if five degree of freedominformation is provided, one of the indicia 82, 84, 86, 88, 90, and 92will be removed.

Once the coordinate system is selected at block 80, the method proceedsto block 108 where the target or trajectory is selected. The target ortrajectory selected at block 108 is typically positioned at the origin102 on the display 10. In this way, the object being tracked or alignedmay be tracked and aligned about the origin 102. Alternatively, thetarget may be identified at any coordinate within the display 10 ormultiple targets may also be identified within the single display 10. Anindicia of the target may also be positioned on the display 10. Thetarget is selected based upon the desired area to position theinstrument 52 and can be selected from the pre-acquired images or fromthe 3-D model. Once selected, this target is correlated to the display10 and generally positioned at the origin 102.

Once the target/trajectory is selected at block 108, such as the origin102, the method proceeds to block 110 where the safe zones areidentified for each degree of freedom. Referring again to FIG. 5, thesafe zones 112 are identified for each degree of freedom by colorcoding. For example, the safe zone 112 for the X axis is between −2.5and +2.5. The safe zone 112 for rotation about the X axis is between −5°and +5° of rotation about the X axis. The user can simply guide theinstrument 52 using the cross hairs 104 and circle 106 to align theinstrument 52 within these designated safe zones 112. Again, these safezones 112 may be determined by manufacture specifications, such astolerance range of the instruments or positions for implants. The safezones 112 may also be determined based on the patient, the surgeonconducting the procedure, or any other factors to assist a surgeon innavigating the instrument 52 through the patient 14. These safe zones112 may also be identified via an audible signal or tone or a varyingtone. The safe zones 112 may also be identified by any other convenientmanner to be set out on the display 10.

Once the safe zones 112 are identified for each degree of freedom inblock 110, the method proceeds to block 114 where the target trajectoryin the selected coordinate system is displayed with the safe zones 112,as shown in FIG. 5. At block 116, if an image based method is beingconducted, a decision whether to superimpose the image over thetarget/trajectory is made. Alternatively, the image may be placedadjacent to the target trajectory display, as is shown in FIG. 6, andfurther discussed herein. Should the image-less based medical procedurebe conducted, at block 118, a determination is made whether tosuperimpose the model that was generated at block 78. Here again, thismodel may be superimposed over the target/trajectory display on display10 or may be positioned adjacent to the target/trajectory display in asplit screen or on a separate display.

Once the target/trajectory 102 is displayed along with the safe zones112 in the proper coordinate system, as shown in FIG. 5, the methodproceeds to block 120 where the first implant/instrument 52 is trackedwith the navigation system 44. With the implant/instrument 52 beingtracked at block 120, the method proceeds to block 122 wherein indiciarepresenting the implant/instrument 52 is displayed on the display 10,with either five or six degrees of freedom information. Here again,referring to FIG. 5, the indicia representing the implant/instrument 52is the crosshairs 104 and the circle 106 designating the tip and hind,respectively. The tip 104 and hind 106 is represented in relation to thetarget/trajectory path 102 in six degrees of freedom. This six degreesof freedom include the X and Y locations, as well as the depth Z of theimplant/instrument 52 displayed. In addition, the rotation about each ofthe axes is also provided. This rotation can be helpful in manyapplications, including orthopedic, where rotation specific componentsneed to be positioned relative to one another. For example, in a spinalapplication, alignment of a pedicle screw in relation to a spinal rod,would require information regarding the rotation of the screw relativeto the rod. In cardiac procedures, this may be useful where ablation isnecessary on a certain side of an artery and the ablation electrode isonly positioned on one side of the catheter. In this situation, rotationof the catheter relative to the target in the artery is critical. In aneuro procedure, a biopsy needle may only have a biopsy port positionedupon one portion of the circumference of the needle, thereby requiringthe rotation of the biopsy needle to be known in order to provide theproper capture of the relevant biopsy sample. Without this display, thisinformation would not be available.

With the indicia of the implant/instrument 52 being displayed, theimplant/instrument 52 is aligned or fixed with the target/trajectory 102at block 124. In this regard, the tip 104 and the hind 106 are alignedand fixed relative to the target/trajectory 102 at the origin and therotational orientation is also aligned to the desired position. Again,the target/trajectory 102 may not be positioned at the origin and can bepositioned anywhere within the coordinate system if desired. As shown inFIG. 5, the tip 104 of the implant/instrument 52 is shown aligned withthe target 102, while the hind 106 is slightly offset from thetarget/trajectory 102. Once the implant/instrument 52 is aligned andfixed relative to the target/trajectory 102, the method proceeds toblock 126.

At block 126, a determination is made as to whether there is a secondimplant/instrument 52 to be tracked. If there is not a secondimplant/instrument 52 to be tracked, the method ends at block 128.Should there be a second implant/instrument 52 to track, such as acorresponding implant component that articulates with the first implant,the method proceeds to block 130. At block 130, a secondtarget/trajectory 102 is selected, which is based upon the alignment orfixation of the first implant/instrument 52 relative to the firsttarget/trajectory 102. In this regard, if the surgeon is not able toposition the first implant/instrument 52 at the desiredtarget/trajectory 102, this offset from the target/trajectory 102 mayaffect the second implant, which possibly articulates or mates with thefirst implant. If this is the case, the second target/trajectory 102will need to take into consideration this offset in order to provideproper articulation and alignment of the first implant component withthe second implant component.

With minimally invasive types of procedures, the implant may also havenumerous components with each component articulating or mating withanother component, thereby requiring tracking of each component as it isimplanted during the minimally invasive procedure. This secondtarget/trajectory 102 may be displayed on a separate display 10 (seeFIG. 1), positioned via a split screen of a single display 10 or may besuperimposed upon the existing display that displays the first target102 and implant position. In this way, orientation and placement of boththe first and second implants, which are dependent upon one another canbe shown in the display 10 providing the surgeon the opportunity toadjust either position of either implant intraoperatively before theimplants are permanently affixed to the patient 14. These types ofimplants include knee implants, hip implants, shoulder implants, spinalimplants, or any other type of implant, which has a bearing surface andan articulating surface or any type of implant having multiple matingand connecting components.

Once the second target/trajectory 102 has been selected at block 130,the method proceeds to block 132. At block 132, the safe zones 112 foreach degree of freedom is selected for the second implant/instrument 52similar to the way the first set of safe zones 112 were selected for thefirst implant/instrument 52. Once the second safe zones 112 areselected, the method proceeds to block 134. At block 134, the display 10displays the second target/trajectory 102 in the same coordinate systemwith the second safe zones 112. Here again, at block 136, if it is animage based medical procedure, the pre-acquired image may besuperimposed on to the target/trajectory 102. Alternatively, this imagecan be positioned adjacent the target screen in a split screenconfiguration (see FIGS. 6 and 7). If the method is proceeding as animage-less type medical procedure, at block 138, decision is madewhether to superimpose the generated model from block 78. Once thetarget/trajectory 102 is in the proper coordinate system with the safezone 112 are displayed at display 10, the surgical implant/instrument 52is tracked at block 140. Here again, the second implant/instrument 52can be tracked on a separate display 10 or be tracked on the samedisplay as the first implant/instrument 52.

Alternatively, separate displays 10 may be used where information islinked between the displays showing the second implant/instrument 52 inrelation to the first implant/instrument 52. With the secondimplant/instrument 52 being tracked at block 140, the secondimplant/instrument 52 is displayed in relation to the secondtarget/trajectory 102 in five or six degrees of freedom at block 142.Again, this may be a separate display 10, a split screen display 10 withboth the first target/trajectory 102 and the second target/trajectory102 or the same display 10 displaying both targets/trajectories 102.While the second implant/instrument 52 is being displayed, the secondimplant/instrument 52 is aligned and fixed at the secondtarget/trajectory 102 at block 144. Once the second implant/instrument52 is fixed at block 144, the method proceeds to block 146.

At block 146, a determination is made whether the alignment or fixationof the first and second implants/instruments 52 are correct. In thisregard, with two separate displays 10 linked or with a single display10, showing both targets/trajectories 102, a surgeon can determinewhether each implant/instrument 52 is within its desired safe zones 112and, therefore, optimally positioned for proper articulation. Hereagain, these safe zones 112 may be color coded for the different safezones provided. If both implants are positioned and fixed at the propertargets, the method ends at block 148. If one or both of the implantsare not properly positioned, adjustment of the first or secondtarget/trajectory 102 is performed at block 150. Once either or bothtargets are adjusted, realignment of the first and/or secondimplants/instruments 52 are performed at block 152. Here again, sincemultiple component implants are dependent upon one another with respectto their position and orientation, alignment and adjustments of thetargets/trajectories 102 may be performed several times until theoptimum placement for each is performed at repeat block 154. Thereafter,the method terminates at end block 156.

While the above-identified procedure is discussed in relation to anorthopedic medical procedure in which an implant having multiple implantcomponents is implanted within a patient using the six degree of freedomdisplay 10, it should be noted that the six degree of freedom display 10may be used to track other medical devices as well. For example, as wasbriefly discussed, an ablation catheter generally has an electrodepositioned only on one angular portion of its circumference. Likewise,the wall of an artery typically has a larger plaque build-up on oneside. Therefore, it is desirable to align that ablation electrode withthe proper side of the artery wall during the procedure. With the sixdegree of freedom display 10, the surgeon can easily identify thelocation, depth and angular rotation of the catheter relative to theartery wall. Other types of procedures may require the medicalinstrument or probe to be properly oriented and located within thepatient, such as identifying and tracking tumors, soft tissue, etc. Byknowing and displaying the six degree of freedom movement of the medicaldevice on the display 10, the medical procedure is optimized.

It should also be pointed out that the method discussed above requiresthat the implant/instrument 52 have a tracking sensor associatedtherewith in order to identify the location of the tracked device in sixdegrees of freedom and display it on the display 10. The trackingsensors may be attached directly to implants, attached to theinstruments that engage the implants or attach to members extending outfrom the implants. These tracking sensors again may be electromagnetictracking sensors, optical tracking sensors, acoustic tracking sensors,etc. Examples of various targets, which may or may not be superimposedon the display again include orthopedic targets, spinal targets,cardiovascular targets, neurovascular targets, soft tissue targets, etc.Specific examples include again the location of the plaque on a wall ofan artery, the center of an articulating joint being replaced, thecenter of the implant placement, etc. By displaying two targets, eitheron separate displays or on the same display, the surgeon can dynamicallyplan and trial implant placements by moving one component of the implantto see where the other articulating component of the implant should bepositioned. In this way, the surgeon can trial the implant confirmingits placement and orientation, via the display 10 before the implant ispermanently affixed to the patient 14.

In a spinal procedure, two adjacent vertebra bodies can be tracked anddisplayed on two separate displays. In this way, if a single jig, suchas a cutting jig is used to cut both the surface of the first vertebraand the surface of the second vertebra, orientation of the jig may bedisplayed on each separate display in relation to the correspondingvertebra being acted upon, thereby enabling simultaneous tracking of thetwo planes being resected for each separate vertebra on a dual displaysystem. Additionally, each vertebra may be displayed on each of the dualdisplays so that the vertebra being tracked is shown with the adjacentvertebra superimposed adjacent thereto. Once the vertebra bodies areprepared, the implant is typically placed between each vertebra on theprepared site. Other ways of preparing this site is by using drills,reamers, burrs, trephines or any other appropriate cutting or millingdevice.

Briefly, the method, as shown in FIGS. 3 a and 3 b, demonstrates thatthe display 10 illustrated both the position and orientation of anobject with respect to a desired position and orientation with sixdegrees of freedom accuracy. The display 10 may be automatically updatedin real-time using the navigation system 44 to report the orientation ofthe tracked device. The user may also adjust the display 10 in order tocontrol a device's orientation. The display 10 again consists of threerotational indicators (RX, RY, RZ) and three translational indicators orindicia (TX, TY, TZ). Each indicator shows both visual and quantitativeinformation about the orientation of the device. Each indicator alsodisplays a predetermined safe zone 112 and application-specific labelfor each degree of freedom. As noted, it may also be relevant to overlaythe display 10 over anatomical image data from the imaging device 16.When working with 3-D image data sets, the anatomy normal to the tip 104of the positioned device can provide the user with additional positionalinformation.

Tones, labels, colors, shading, overlaying with image data can all bemodified and incorporated into the display 10. The current display 10 isalso shown as a Cartesian coordinate based display, but again could bebased on a polar based display or a spherical based display and a quickswitch between both can be supplied or simultaneously displayed. Thedisplay can also be configured by the user to hide parameters, location,size, colors, labels, etc.

Some medical applications that may be commonly displayed and linked tothe display 10 are: 1) reaming of an acetabular cup with major focusupon RY and RZ, 2) length of leg during hip and knee procedures focusedupon TZ and RZ, 3) biopsies and ablations focused upon RX, RY, and RZfor direction of the therapy device, and 4) catheters with side portsfor sensing information or delivery of devices, therapies, drugs, stemcells, etc. focused upon six degree of freedom information.

Referring now to FIGS. 4 a-4 e, a medical procedure employing a sixdegree of freedom alignment display 10 is shown in further detail. Inthis example, an orthopedic medical procedure replacing the hip joint isillustrated. During this procedure, various instruments 52, as well asthe implants 52 are tracked and aligned using the six degree of freedomdisplay 10. Referring specifically to FIG. 4 a, a femur 160 having afemoral head 162 is illustrated, along with a pelvis 164 having anacetabulum 166. Assuming that the medical procedure being performed isan image based system, this area of interest will be imaged by theimaging device 16. Here again, the dynamic reference frame 54 may beattached to the femur 154 or the pelvis 164 or two dynamic frames 54 maybe attached, one to each bone to provide additional accuracy during themedical procedure. With the head 162 dislocated from the acetabulum 166,a center of articulation of the acetabulum 166 is identified as thetarget 168, shown in FIG. 6.

In this regard, FIG. 6 illustrates the display 10 configured as a splitscreen with the right identifying the six degree of freedom display andthe left illustrating the pre-acquired image with the center ofarticulation 168 being the intersection of the X, Y, and Z axes. Asillustrated in FIG. 4 a, a reamer 170 having a tracking sensor 58 isshown reaming the acetabulum 166. The tracking system 44 is able toaccurately identify the navigation of the tip and hind of the reamer170. As illustrated in FIG. 6, in the right half of the split screen,one can observe that the tip represented by the crosshairs 172 isproperly positioned along the X and Y coordinates and within thecorresponding safe zones 112, however, the hind portion of theinstrument 170, as identified by the circle 174, is angularly offsetfrom the target 168 at the origin. The surgeon can then angularly adjustthe hind portion 174 of the instrument 170 until the hind portion 174 isshown in the display 10 as positioned over the crosshairs 172, therebyassuring proper alignment of the reaming device 170 for subsequentproper placement of the acetabular cup implant. By tracking the reamer170, the surgeon can be relatively confident that an acetabular cupimplant will be properly positioned before the implant is even impactedinto the acetabulum 166.

Turning to FIG. 4 b, an acetabular cup 178 is shown being impacted intothe reamed acetabulum 166, via the tracked guide tool 180 with animpactor 182. The guide tool 180 has a distal end, which is nestinglyreceived within the acetabular cup 178. Thus, by tracking the instrument180, via tracking sensor 58, orientation of the acetabular cup 178 maybe displayed on the display 10 in six degrees of freedom. In this way,before the acetabular cup 178 is impacted into the acetabulum 166, thesurgeon can view on the display 10 whether the acetabular cup 178 isproperly positioned at the proper angular orientation, as shown in FIG.7, the impactor 180 is shown superimposed over an image generated by theimaging device 16. In this way, the proper orientation, includingabduction and anteversion is achieved before the acetabular cup 178 ispermanently implanted.

Once the acetabular cup 178 has been impacted, the femoral head 162 isresected along a plane 184 by use of a cutting guide 186, having thetracking sensor 58 and a saw blade 188. By using the center of thefemoral head 162 as the second target, the cutting plane 184 may beproperly defined to provide proper articulation with the acetabular cup178 before a hip stem is implanted in the femur 160. Here again, thesecond target is dependent upon the first target. Thus, if theacetabular cup 178 was implanted somewhat offset from its target, thesecond target may be properly compensated to accommodate for this offsetby use of the display 10. In this regard, a second display illustratingthe target for the cutting plane 184 may be provided.

Once the femoral head 162 of the femur 160 has been resected, as shownin FIG. 4 d, a reamer 190 is employed to ream out the intramedullarycanal 192 of the femur 160. In order to provide proper angularorientation of the reamer 190, as well as the depth, a subsequent targetcan be defined and identified on the display 10 and tracked by use ofthe tracking sensor 58. This target may be displayed separately or incombination with the previously acquired targets. By insuring the properangle of the reamer 190 relative to the longitudinal axis of the femur160 is tracked and displayed on display 10, the surgeon can be provideda higher level of confidence that the hip stem will be properlypositioned within the intramedullary canal 192.

Once the intramedullary canal 192 has been reamed by the reamer 190, ahip stem 194 is impacted with an impactor 196 into the intramedullarycanal 192. By targeting the acetabular cup location, along with theresection plane 184 and the reaming axis of the reamer 190, uponpositioning the hip stem 194, within the femur 160, proper articulationand range of motion between the acetabular cup 178 and the hip stem 194is achieved without time consuming trialing as is conducted inconventional orthopedic procedures. Thus, by providing the safe zones112 in relation to the hip stem 194 size, proper articulation with theacetabular cup 178 is achieved. Here again, while an example of anorthopedic hip replacement is set out, the six degree of freedom display10 may be utilized with any type of medical procedure requiringvisualization of a medical device with six degree freedom information.

The six degree of freedom display 10 enables implants, devices andtherapies that have a specific orientation relative to the patientanatomy 14 to be properly positioned by use of the display 10. As wasnoted, it is difficult to visualize the correct placement of devicesthat require five or six degree of freedom alignment. Also, theorientation of multiple-segment implants, devices, or therapies in fiveand six degrees of freedom so that they are placed or activated in thecorrect orientation to one another is achieved with the display 10.Since the location and orientation is dependent upon one another to beeffective, by having the proper orientation, improved life of theimplants, the proper degrees of motion, and patient outcome is enhanced.Also, the six degree of freedom display 10 may be used as a user inputmechanism by way of keyboard 38 for controlling each degree of freedomof a surgical robotic device. In this regard, the user can inputcontrols with the joystick, touch screen or keyboard 38 to control arobotic device. These devices also include drill guide holders, drillholders, mechanically adjusted or line devices, such as orthopediccutting blocks, or can be used to control and drive the alignment of theimaging system 16, or any other type of imaging system.

Since multiple implants and therapies, or multi-segment/compartmentimplants require multiple alignments, the display 10 may include astereo display or two displays 10. These displays may or may not belinked, depending on the certain procedure. The target point/location(translation and orientation of each implant component is dependent uponthe other implant placement or location). Therefore, the adjustment ordynamic targeting of the dependent implant needs to be input to thedependent implant and visually displayed. Again, this can be done by twoseparate displays or by superimposing multiple targets on a singledisplay. Many implants such as spinal disc implants, total knee andtotal hip replacements repair patient anatomy 14 by replacing theanatomy (bone, etc.) and restoring the patient 14 to the originalbiomechanics, size and kinematics. The benefit of the six degree offreedom alignment display 10 is that original patient data, such as theimages can be entered, manually or collectively, via the imaging device16 or image-less system used for placement of the implant. Again,manually, the user can enter data, overlay templates, or collect data,via the imaging system 16. An example, as discussed herein of anapplication is the alignment of a femoral neck of a hip implant in theprevious patient alignment. The previous patient alignment can beacquired by landmarking the patient femoral head by using biomechanicsto determine the center and alignment of the current line and angle ofthe femoral head. This information can be used as the target on thedisplay 10 in order to properly align the implant replacing the femoralhead.

The six degree of freedom display 10 also provides orientation guidanceon a single display. Separate visual and quantitative read-outs for eachdegree of freedom is also displayed on the display 10. Visualrepresentations or indicia of procedure-specific accepted values (i.e.,a “safe zone 112”) for each degree of freedom is also clearly displayedon the display 10. These safe zones 112 are displayed as specifics orranges for the user to align or place within. The procedure specificaccepted values for the safe zones 112 can be manufacture determined,user determined, patient specific (calculated) or determined fromalgorithms (finite element analysis, kinematics, etc. atlas or tables).It can also be fixed or configurable. Safe zones 112 can also be definedas ranges around a planned trajectory path or the specific trajectorypath itself (range zero). The trajectory paths are input as selectedpoints by the user or paths defined from the patient image data(segmented vascular structure, calculated centers of bone/joints,anatomical path calculated by known computed methods, etc.).

Turning now to FIGS. 8 a-8 g, another medical procedure employing thesix degree of freedom alignment display 10 is shown in further detail,along with FIG. 9 illustrating the use of the display 10 during thismedical procedure. In this example, a spinal medical procedure thatimplants a cervical disc implant between two vertebrae is illustrated.During this procedure, various instruments 52, as well as the implant 52are tracked and aligned using the six degree of freedom display 10.Also, the bony structures during the procedure are also tracked.

Referring specifically to FIG. 8 a, a first vertebra or vertebral body200 is shown positioned adjacent to a second vertebra or vertebral body202 in the cervical area of the spine. Assuming that the medicalprocedure is being performed in an image based system, this area ofinterest would be imaged by the imaging device 16. Again, a dynamicreference frame 54 may be attached to the first vertebra 200 and asecond dynamic reference frame 54 may be attached to the second vertebra202. These dynamic reference frames 54 may also be combined withtracking sensors 58, which are shown attached to the vertebral bodies200 and 202. A center of articulation of the vertebra 200 and a centerof articulation of a vertebra 202 may be identified as the targets 168on the dual display illustrated on FIG. 9. In this way, by utilizing thecenter of articulation of each vertebral body with respect to each otheras the targets 168, tracking of the instruments 52 used during theprocedure, as well as the implant 52 with respect to these articulationcenters may be achieved.

Referring to FIG. 8 b, a cam distracter instrument 204 is showndistracting the vertebra 200 relative to the vertebra 202. The camdistracter 204 may be tracked, via another tracking sensor 58 affixed tothe cam distracter 204. In this way, the six degree of freedom display10 illustrated in FIG. 9 can illustrate a location of the cam distracter204 relative to the center of each vertebra 200 and 202 independently onthe display. Since the instrument 204 is rigid, by locating the trackingsensor 58 on the instrument 204, the distal end of the instrument 204 isknown and may be illustrated on the display 10 using crosshairs 104 andcircle 106 to represent the tip and hind, respectively.

Once each vertebrae 200 and 202 have been distracted by the camdistracter 204, a sagittal wedge 206 also having a tracking sensor 58 isutilized and shown in FIG. 8 c. The sagittal wedge 206 is used to centereach vertebrae 200 and 202, along the sagittal plane and again may betracked and displayed with six degree of freedom on the display 10, asillustrated in FIG. 9. In this regard, the surgeon can confirm bothvisually and via the display 10 that the sagittal wedge 206 is centeredon the sagittal plane between the vertebrae 200 and 202, as well asobtain the proper depth, via the Z axis display 86 on the display 10,illustrated in FIG. 9.

Once the sagittal centering has been achieved with the sagittal wedge206, the medical procedure proceeds to burring as shown in FIG. 8 d. Inthis regard, a burr 208 attached to a burring hand piece 210, alsohaving a tracking sensor 58, is used to burr an area between the firstvertebra 200 and the second vertebra 202. Here again, the orientation ofthe burr 208 relative to each vertebrae 200 and 202 may be displayed onthe display 10 with six degree of freedom information. Therefore,burring along the proper X and Y plane, as well as the proper depth maybe visually displayed with the appropriate indicia, as illustrated inFIG. 9. Rotational information about the corresponding X, Y and Z axesis also displayed. By burring within the safe zones 112 using theinformation regarding the surgical implant 52 as the safe zones 112, thesurgeon can be assured to perform the proper burring between thevertebrae 200 and 202 to insure a proper oriented fit for the surgicalimplant 52. By tracking the burr 208 with six degrees of freedominformation, the mounting anchors 212 for the hand piece 210 areoptional and may not be required. Additionally, each single display inthe dual display 10, as shown in FIG. 9, may also superimpose an imageof each vertebrae 200 and 202 relative to one another on the displaywith each display having its coordinate system referenced to one of thevertebrae. The resulting milled vertebrae 200 and 202 are shown in FIG.8 e with a ring portion 214 milled to receive the spinal implant 52.

Referring to FIGS. 8 f and 8 g, the spinal implant 52 is shown beingimplanted between the vertebrae 200 and 202 using an implant inserter216 that is also tracked by tracking sensor 58. By tracking the implantinserter 216 relative to the vertebrae 200 and 202, proper orientationof the spinal implant 52, as well as rotational orientation about the Zaxis can be clearly displayed on the six degree of freedom display 10,as shown in FIG. 9. Rotation about the Z axis is used to make sure thatthe flanges 218 of the implant 52 are properly oriented and centeredalong the sagittal plane, as shown in FIG. 8 g. Again, by using thedisplay 10, as illustrated in FIG. 9, the anchors 220 are optional sinceorientation of the implant 52 can be tracked continuously as it isinserted between the vertebrae 200 and 202. Here again, this eliminatesthe need for forming holes in the vertebrae 200 and 202. It shouldfurther be noted that the implant 52 illustrated in these figures ismerely an exemplary type of spinal implant and any known spinal implantsmay also be similarly tracked. For example, another common type ofspinal implant is formed from a two-piece unit that includes a ball andcup articulating structure that may likewise be independently tracked toassure proper fit and placement.

Here again, the six degree of freedom display 10, which is illustratedas a split or dual display 10 in FIG. 9 assists a surgeon in implantinga spinal implant 52 in order to achieve proper fixation and orientationof the implant 52, relative to two movable vertebrae 200 and 202. Bytracking each vertebra 200 and 202 independently, and tracking itsresection, should one vertebra be resected off-plane due to anatomicalanomalies, adjustment of the plane at the adjacent vertebra may beachieved in order to still provide a proper fit for the spinal implant52. In this way, each vertebrae 200 and 202 can be independentlymonitored, so that if one is off axis, the other can be manipulatedaccordingly to account for this adjustment. Additionally, by monitoringthe entire process having six degree of freedom information, via display10, further accuracy was achieved, thereby providing increased range ofmotion for the patient after implantation of the implant 52.

By use of the six degree of freedom display, for the various types ofmedical procedures, improved results can be achieved by providing thesurgeon with the necessary information required. In regard to surgicalimplants, the range of motion may be increased while reducingimpingement of two-part articulating or fixed implants. This alsoenables maximum force transfer between the implant and the body. Withtherapy delivery procedures, by knowing the location of the catheterdelivery tube and the specific port orientation, accurately aiming atthe site is enabled to provide maximum delivery of the therapy at thecorrect site. This procedure also enhances and enables better resultswhen using an ablation catheter by again knowing the rotationalorientation of the ablation catheter and the ablation electrode relativeto the area in the wall of the artery that requires ablation. Finally,by knowing the rotational orientation of a ablation or biopsy catheter,this type of catheter may be easily directed and aligned to tumors, stemcells, or other desired sites in an easy and efficient manner.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A navigation system for guiding a medical device to a target in apatient during a medical procedure, said navigation system comprising: adisplay; and a workstation operably connected to the display andconfigured to process information from: a tracking sensor associatedwith the medical device and operable to be used to track the medicaldevice, and a tracking device operable to track the medical device withthe tracking sensor to update a position of the medical device as themedical device is guided, the workstation, in response to the positionof the medial device, configured to provide information for displayingon the display: a first indicia identifying a first degree of freedominformation; a second indicia identifying a second degree of freedominformation; a third indicia identifying a third degree of freedominformation; a fourth indicia identifying a fourth degree of freedominformation; and a fifth indicia identifying a fifth degree of freedominformation; a sixth indicia identifying a sixth degree of freedominformation; and wherein said first, second, third, fourth, fifth andsixth indicia are illustrated on said display to assist in guiding themedical device to the target, the first, second, and third indicia areX, Y, and Z axes, respectively, with said X axis represented by ahorizontal bar, said Y axis represented by a vertical bar crossing saidX axis, and said Z axis represented by a separate bar, with a positionof the medical device as the medical device is guided represented by anarrow on each of the displayed X axis, Y axis, and Z axis, and thefourth, fifth, and sixth indicia are rotation about the X, Y, and Zaxes, respectively.
 2. The navigation system as defined in claim 1wherein the indicia are illustrated in a coordinate system selected froma group comprising a Cartesian coordinate system, a spherical coordinatesystem, a polar coordinate system, and a combination thereof.
 3. Thenavigation system as defined in claim 1 wherein at least one of theindicia illustrates a safe zone in relation to said corresponding degreeof freedom information.
 4. The navigation system as defined in claim 3wherein each indicia illustrates a safe zone.
 5. The navigation systemas defined in claim 3 wherein said safe zone is illustrated by way ofcolor, audible tones, cross-hatching and a combination thereof.
 6. Thenavigation system as defined in claim 1 wherein the workstation furtherdisplays on the display an indicia of a tip portion of the medicaldevice and an indicia of a hind portion of the medical device depictingthe relative position and orientation of the medical device.
 7. Thenavigation system as defined in claim 1 wherein rotation about the Xaxis is illustrated by a straight bar graph having an arrow identifyingthe amount of rotation, wherein the rotation about the Y axis isillustrated by a straight bar graph having an arrow illustrating theamount of rotation about the Y axis and the rotation about the Z axis isillustrated by an arcuate bar graph having an arrow illustrating therotation about the Z axis.
 8. The navigation system as defined in claim1 wherein the workstation further displays on the display atarget/trajectory indicia identifying the target/trajectory for themedical device.
 9. The navigation system as defined in claim 8 whereinthe workstation further displays on the display indicia of a secondtarget/trajectory identifying a second target/trajectory.
 10. Thenavigation system as defined in claim 8 wherein said target indicia isan origin.
 11. The navigation system as defined in claim 1 wherein theworkstation further displays on the display at least one of an image ofthe patient superimposed on said display and one of a model of thepatient superimposed on said display.
 12. The navigation system asdefined in claim 1 wherein said display includes multiple displays. 13.The navigation system as defined in claim 1 wherein the workstationdisplays on the display said first, second, third, fourth and fifthindicia simultaneously.
 14. The navigation system as defined in claim 1wherein said display assists in the control of a surgical robot usedduring the medical procedure.
 15. The navigation system as defined inclaim 1 wherein the workstation further displays on the display a safezone that is illustrated as a region of a first color on each of thebars different than a second color of the remaining portion of each bar.16. The navigation system of claim 1, wherein the workstation furtherdisplays on the display a position of the instrument that is illustratedas an icon on a single display with the each of the bars and operable tobe displayed separate from each of the bars.
 17. The display navigationsystem of claim 1, wherein each of the degree of freedom informationindicates a position of the instrument within a Cartesian coordinatesystem; wherein the first degree of freedom information is a X axisposition of the instrument, the second degree of freedom information isa Y axis position of the instrument, the third degree of freedominformation is a Z axis position of the instrument, the fourth degree offreedom information is a rotation around the X axis of the instrument,the fifth degree of freedom information is a rotation around the Y axisof the instrument, and the sixth degree of freedom information is arotation around the Z axis of the instrument.
 18. The navigation systemof claim 1, wherein the display includes a human viewable display havinga width and a height; wherein the X axis bar and the Y axis bar arepositioned near a center of the display, the Z axis bar extends out fromthe display and is shown in an upper left corner, rotation about the Xaxis is shown by bar graph on a right of the display, rotation about theY axis is shown by bar graph positioned at the bottom of the display,rotation about the Z axis is shown with an arcuate bar graph orientedabout the X and Y axes.
 19. A navigation system for use in guiding amedical device to a target in a patient during a medical procedure, saidnavigation system comprising: a tracking sensor associated with themedical device and operable to be used to track the medical device; atracking device operable to track the medical device with the trackingsensor to update a position of the medical device as the medical deviceis guided; and a workstation having a display, the workstationconfigured to provide information data for displaying on the displayindicia illustrating at least five degrees of freedom information andindicia of the position of the medical device in relation to said atleast five degrees of freedom information as the medical device isguided; wherein the first, second, and third indicia are X, Y, and Zaxes, respectively, with the X axis represented by a horizontal bar, theY axis represented by a vertical bar crossing the X axis, and the Z axisrepresented by a separate bar, with the position of the medical devicerepresented by an arrow on each of the displayed X axis, Y axis, and Zaxis.
 20. The navigation system as defined in claim 19 wherein saidtracking sensor is attached to the medical device.
 21. The navigationsystem as defined in claim 19 wherein said tracking sensor is selectedfrom a group comprising an electromagnetic sensor, an optical sensor, anoptical reflector, an electromagnetic transmitter, a conductive sensor,an acoustic sensor, or combinations thereof.
 22. The navigation systemas defined in claim 19 wherein said tracking device is selected from agroup comprising an electromagnetic tracking device, an optical trackingdevice, a conductive tracking device, an acoustic tracking device, orcombinations thereof.
 23. The navigation system as defined in claim 19further comprising an imaging device operable to generate image data ofa region of the patient.
 24. The navigation system as defined in claim19 wherein said navigation system has an image-less based navigationsystem wherein said image-less navigation system is operable to generatea model representing a region of the patient.
 25. The navigation systemas defined in claim 19 further comprising a dynamic reference frameattached to the patient and operable to be used to track movement of thepatient relative to said tracking device.
 26. The navigation system asdefined in claim 19 wherein the medical device is a medical instrumentor implant.
 27. The navigation system as defined in claim 19 whereinsaid indicia of the medical device includes indicia identifying a tipportion and indicia identifying a hind portion of the medical device.28. The navigation system as defined in claim 27 wherein said tipincludes indicia of crosshairs and said hind includes indicia of acircle.
 29. The navigation system as defined in claim 19 wherein saidmedical device is a device having at least a first component and asecond component where placement of said first component is dependentupon placement of said second component and wherein said display isoperable to display proper position of said first component relative tosaid second component.
 30. The navigation system as defined in claim 19,wherein at least three of the of the five degree of freedom informationis illustrated on the display; and wherein a first degree of the fivedegree of freedom information includes the X axis represented by thehorizontal axis bar and a second degree of the five degree of freedominformation includes the Y axis represented by the vertical axis barcrossing the X axis bar, wherein a position of the medical device isillustrated by a cross-hair relative to the axis bars.
 31. Thenavigation system as defined in claim 30, wherein rotation of themedical device about the X axis is illustrated by a straight bar graphhaving an arrow identifying the amount of rotation, wherein the rotationabout the Y axis is illustrated by a straight bar graph having an arrowillustrating the amount of rotation about the Y axis, and the rotationabout the Z axis is illustrated by an arcuate bar graph having an arrowillustrating the rotation about the Z axis.
 32. The navigation system ofclaim 31, wherein the display includes a human viewable display having awidth and a height; wherein the X axis bar and the Y axis bar arepositioned near a center of the display, the Z axis bar extends out fromthe display and is shown in an upper left corner, rotation about the Xaxis is shown by bar graph on a right of the display, rotation about theY axis is shown by bar graph positioned at the bottom of the display,rotation about the Z axis is shown with an arcuate bar graph orientedabout the X and Y axes.
 33. The navigation system of claim 19, wherein aposition of the medical device is illustrated as an icon on a singledisplay with the each of the bars and operable to be displayed separatefrom each of the bars.
 34. The navigation system of claim 19, whereineach of the five degrees of freedom information indicates a position ofthe medical device within a Cartesian coordinate system; wherein threeof the degrees of freedom include the first degree of freedominformation is a X axis position of the medical device, the seconddegree of freedom information is a Y axis position of the medicaldevice, the third degree of freedom information is a Z axis position ofthe medical device; wherein two of the degrees of freedom include atleast two of the fourth degree of freedom information is a rotationaround the X axis of the medical device, the fifth degree of freedominformation is a rotation around the Y axis of the medical device, thesixth degree of freedom information is a rotation around the Z axis ofthe medical device, and combinations thereof.
 35. A method fornavigating and displaying a medical device during a medical procedure,said method comprising: selecting a target for navigating the medicaldevice to; displaying the target in a coordinate system that includes anX axis represented by a horizontal bar, a Y axis represented by avertical bar crossing the X axis, and a Z axis represented by a separatebar; tracking the medical device with a navigation system to determine aposition of the medical device in the coordinate system; and displayingthe medical device in relation to the target with at least five degreesof freedom information by displaying an indicia that indicates theposition of the medical device on each of the X axis, Y axis and Z axisas the medical device is navigated.
 36. The method as defined in claim35 further comprising selecting a safe zone for at least one of thedegrees of freedom information.
 37. The method as defined in claim 36further comprising selecting a safe zone for each degree of freedominformation.
 38. The method as defined in claim 35 further comprisingaligning the medical device with the target using the five degree offreedom information.
 39. The method as defined in claim 35 furthercomprising selecting a second target that is positioned in relation tothe first target for a second medical device; and displaying the secondtarget in the coordinate system.
 40. The method as defined in claim 39further comprising: tracking the second medical device; and displayingthe second medical device in relation to the second target with the atleast five degree of freedom information.
 41. The method as defined inclaim 40 further comprising aligning the second medical instrument withthe second target.
 42. The method as defined in claim 41 furthercomprising: determining whether the alignment of the first medicaldevice and the second medical device are correct; and realigning thefirst medical device, the second medical device, or combinations thereofwhen the alignment is determined to be incorrect.
 43. The method asdefined in claim 35 wherein selecting the target further includesselecting a center of a joint.
 44. The method as defined in claim 35wherein selecting the target further includes selecting a target basedupon an articulating plane of a joint.
 45. The method as defined inclaim 35 wherein selecting the target further includes selecting an areabetween a first vertebra and a second vertebra for placement of animplant.
 46. The method as defined in claim 35 wherein selecting thetarget further includes selecting a site within an artery.
 47. Themethod of claim 35, wherein displaying indicia includes: displaying theX axis as a first degree of the five degree of freedom informationrepresented by the horizontal axis bar and a displaying the Y axis as asecond degree of the five degree of freedom information represented bythe vertical axis bar crossing the X axis bar, wherein a position of themedical device is illustrated by a cross-hair relative to the axis bars;displaying the Z axis as a third degree of the five degree of freedominformation represented by the separate axis bar having an arrowidentifying the position along the Z axis.
 48. The method of claim 47,further comprising at least one of: displaying rotation of the medicaldevice about the X axis by a straight bar graph having an arrowidentifying the amount of rotation; displaying rotation of the medicaldevice about the Y axis by a straight bar graph having an arrowillustrating the amount of rotation about the Y axis; displayingrotation of the medical device about the Z axis by an arcuate bar graphhaving an arrow illustrating the rotation about the Z axis; orcombinations thereof.
 49. The method of claim 47, wherein a position ofthe medical device is represented by an arrow relative to each of thedisplayed X axis bar, Y axis bar, and Z axis bar.
 50. The method ofclaim 47, wherein a position of the medial device is illustrated as anicon on a single display with the each of the bars and operable to bedisplayed separate from each of the bars.
 51. The display of claim 47,further comprising: providing a human viewable display having a widthand a height; positioning the X axis bar and the Y axis bar near acenter of the display positioning the Z axis bar as extending out fromthe display and in an upper left corner of the display; positioning abar graph illustrating rotation about the X axis on a right of thedisplay; positioning a bar graph illustrating rotation about the Y axisat the bottom of the display; and positioning an arcuate bar graphillustrating rotation about the Z axis oriented about the X axis and Yaxis bars.
 52. The display of claim 35, wherein each of the five degreesof freedom information indicates a position of the medical device withina Cartesian coordinate system; wherein three of the degrees of freedominclude the first degree of freedom information is a X axis position ofthe medical device, the second degree of freedom information is a Y axisposition of the medical device, and the third degree of freedominformation is a Z axis position of the medical device; wherein two ofthe degrees of freedom include at least two of the fourth degree offreedom information is a rotation around the X axis of the medicaldevice, the fifth degree of freedom information is a rotation around theY axis of the medical device, the sixth degree of freedom information isa rotation around the Z axis of the medical device, or combinationsthereof.